Study On Safety Risk Analysis Method Of Earth-rock Dam

Overtopping, seepage, and slope instability are the main causes of dam failures. This study takes Wohushan Dam as a case study of three potential failure modes.Based on the theory of risk analysis,this study develops a LHS–MC method to evaluate dam overtopping probability that accounts for the uncertainties arising from wind speed and peak flood. For complex problems, the Monte Carlo (MC) simulation is the most used method in risk analysis. But the conventional MC sampling method is not computationally efficient for rare event problems. Latin hypercube sampling (LHS) is suggested as a tool to improve the efficiency of MC random sampling method. LHS method is used to generate samples of peak flow rate and wind speed especially for rare events. One example of dam overtopping risk analysis is presented to demonstrate the validity and capability of the proposed method. It is shown that LHS method is more efficient than MC simulation,which tends to convergence within relative few simulation times. Reservoir routing, which incorporates operation rules, wind setup, and run-up, is used to evaluate dam overtopping probability.Fault tree analysis (FAT) is used to analysis the failure types of earth-rock dam, and failure modes of earth-rock dam are classified into three main failure mode: overtopping failure mode, seepage failure mode and slope instability failure mode. Risk assessment models for each failure mode are established, and accordingly performance function of each failure mode of dam is proposed.Risk analysis of slope instability in earth dams is presented using LHS–MC method. Latin hypercube sampling (LHS) is suggested as a tool to improve the efficiency of MC random sampling method. Based on the limit equilibrium method,a combination of LHS and MC method is used to evaluate the slope instability risk accounting for the uncertainties arising from soil properties and water level. One example is presented to demonstrate the validity and capability of the proposed method. By means of numerical example, it is shown that about 30% of the calculations can be saved by using LHS–MC method instead of simple MC. The exact savings, however, are dependent on details in the use of LHS and on the shape of the failure surfaces of the problems.The basic principle of the Bayesian network is briefly introduced and compared with the fault tree analysis. A procedure to transform a fault tree into a Bayesian network is presented. Then the Bayesian network is applied to evaluate the reliability of earth-rock dams. The results indicate that the reliability of earth-rock dams can be evaluated using the Bayesian network in a more rational way.